Process for impregnating an adsorbent catalyst with a radioactive metal isotope



y 1966 w. A. WILSON ET AL 3,252,916

PROCESS FOR IMPREGNATING AN ADSORBENT CATALYST WITH A RADIOACTIVE METALISOTOPE Original Filed June 30. 1960 Fig. I

E Q a Q Q g k 3 w 7 ENE/P6) 0v /0 51 95 RETENTION 2F CATALYST a F lg. 23 E i 5 E INVENTORSI Arthur C. Harrington William A. Wilson DAYS BY ATTOR/VEY United States Patent Original application June 30, 1960, Ser.No. 39,901, now

Patent N0. 3,149,233, dated Sept. 15, 1964. Divided and this applicationSept. 13, 1962, er. No. 227,625 5 Claims. (Cl. 252301.1)

This is a division of application Serial No. 39,901, filed June 30,1960, and entitled Chemical Process, now US. Patent No. 3,149,233,granted Sept. 15, 1964.

This invention relates to the conversion of hydrocarbons with fluidizedsolid catalysts, and more particularly concerns methods of studying theperformance of such units. In more detail, the invention provides amethod for determining catalyst loss rates from fluid catalyticconversion units.

In the operation of fluid catalytic conversion units such as fluidcatalytic crackers, it is frequently necessary to measure and study thecatalyst loss rate. Not only is excessive catalyst loss expensive, butinformation pertaining to its is invaluable for analyzing overall unitperformance.

However, the measurement of fluid catalyst loss rate is possibly one ofthe most diiiicult of all material balances. Not only is catalyst lostvia flue gas stacks and the like, but a portion at least is carried outin the cracked hydrocarbon product stream. Moreover, catalyst particlesize distribution is constantly being changed by attrition.

It has previously been proposed to measure catalyst loss, or itscorrelative opposite, catalyst retention, by tagging portions of thecatalyst inventory with radioactive isotopes and following the course ofcatalyst disappearance by measuring the progressive reduction inradiation level. However, radioisotopes are rarely absolutely pure, andthe contribution of each isotope to total radioactivity may changeradically with time, depending on the relative decay rates of theisotopes. It has been proposed to minimize this effect by using a longhalf life isotope, with, however, attendant longterm contaminationproblems. Neither alternative is really satisfactory.

In accordance with the invention we have discovered a method wherebyeven short half life radioisotopes may 'be used in catalyst loss orretention studies without requiring unduly complex mathematicaltreatment to allow for normal radioactive decay. Moreover, our methodpermits simultaneous loss measurements on several different catalystsamples within the same fluidized catalytic conversion unit. We alsoprovide a method whereby the finely divided adsorbent solids which areemployed as conversion catalysts may be uniformly impregnated withradioactive metal isotopes.

Briefly, we uniformly impregnate samples of one or more finely dividedadsorbent solid catalysts with different radioactive metal isotopes eachhaving a distinguishable energy spectrum. Portions of each catalyst areretained, while the balance is introduced into a fluid catalyticconversion unit such as a cat cracker, a fluid hydroformer, or the like.Periodically, catalyst samples are withdrawn from the inventory of theunit, and the energy spectrum of these inventory samples are determined,as by means of a multi-channel pulse height analyzer. At substantiallythe same time, i.e., sufiiciently close in time that the same isotopewill have decayed to substantially the same extent in the retained andin the inventory samples, the energy spectrum of each of the retainedportions are also analyzed. The contribution to the inventory sampleradioactivity by each of the different radioactive metal isotopes,corresponding to the relative proportion of each originally impregnatedcatalyst sample to the total inventory, is then determined as by directcurve substraction or by means of a computer technique hereinafterdisclosed. Thus, by determining the amount of each originallyimpregnated catalyst sample in the inventory it is possible to measurethe loss rates of one, two or many more catalysts. Also, since theanalysis or counting of each sample is performed concurrently with theanalysis of the retained samples, an isotope in each sample will decayto substantially the same extent and the need for correcting forradioactive decay rates is obviated entirely.

We also provide a novel technique for uniformly impregnating finelydivided adsorbent solids with radioactive isotopes. Heretofore this hasbeen a major stumbling block in tracer monitoring of fluid catalyticconversion units, since the individual catalyst particles may range insize from less than ten microns to over two hundred microns. By ourtechnique, every particle size fraction is impregnated with radioactivematerial to a uniformity of within 15% over the range of 40 to microns.In accordance with this aspect of the invention, we form a slurry of thefinely divided absorbent solid catalyst, or other similar solidmaterial, with an inert volatile organic liquid. We separately prepare asolution of a radioactive metal isotope, advantageously in the form of asoluble coordination compound in another inert volatile organic liquidwhich is miscible with the first mentioned liquid; the two liquids maybe either the same or different substances. The slurry and solution arethen intimately mixed to permit the solids to adsorb the dissolvedisotope, after which excess liquid may be removed and the resultantimpregnated solid then dried. This technique aflords the outstandingadvantages of not altering any of the chemical or physical properties ofthe original solid, factors which are crucial in any meaningful studiesof catalyst loss rate.

The invention will be more fully described in the en suingspecification, when read in conjunction with the attached drawingswherein:

FIGURE 1 depicts a typical multi-channel spectra analysis of the emittedgamma energy from several radioisotopes having distinguishable energyspectra together with a typical composite corresponding to a mixture ofthe radioisotopes in the inventory of a fluid catalytic conversion unit;and

FIGURE 2 shows the results of a test wherein the relative loss rates ofthree different commercial cracking catalysts in an operating catalyticcracking unit are determined.

Catalyst impregnation In any tracer study of fluid catalytic conversionunits, it is essential that the portion of catalyst which is tagged witha radioisotope have physical and chemical properties which are identicalto the untagged catalyst. For this reason, any impregnation techniquemust not affect the catalyst. Accordingly, a technique has beendeveloped whereby a catalyst may be tagged with virtually any desiredconcentration of virtually any radioactive metal isotope, without anynoticeable alteration of catalyst properties.

In brief, a finely divided absorbent solid such as a silica-aluminacracking catalyst is slurried with an inert volatile organic liquid. Bythe term inert we designate those liquids which are not decomposed bycontact with the catalyst, and which do not chemically react with it.For example, others such as diethyl ether, alcohols such as methanol,hydrocarbons such as hexane,

3 ketones such as methyl ethyl ketone, and similar liquids may beemployed. The liquid should be sufliciently volatile to permit itsremoval from the catalyst after impregnation treatment without the useof undue temperatures.

Radioactive metal isotopes are commonly available from such sources asthe US. Atomic Energy Commission as inorganic salts in aqueous solution.The metals are advantageously extracted from the aqueous solution intoan immiscible organic liquid such as diethyl ether preferably in theform of a soluble coordination compound (see Bailar, Chemistry of theCoordination Compounds, ACS Monograph 131, Reinhold).

The slurry of solids in the organic liquid, and the solution ofradioisotope in organic liquid (which may be the same or differentliquid from the liquid first mentioned) are then intimately mixed,advantageously with constant stirring. Temperatures for this step areadvantageously at the boiling point so as to secure the benefits ofhaving a mobile liquid. Impregnation occurs rapidly and virtuallyquantitatively. Excess liquid may be decanted off, and the impregnatedsolids are then dried.

As an example of an impregnation procedure along the lines previouslydescribed, zirconium95 is impregnated onto a 12% alumina crackingcatalyst. The isotope is available as a mixture of zirconium-95 andniobium-95 as the oxalates in about 0.5% aqueous oxalic acid.Radioactivity is more than one mc./ml. The solution is wetashed withperchloric acid to remove traces of fluoride and oxalate ions which willinterfere with the subsequent extract-ion. The final wet ash is dilutedto 20 ml. with one M nitric acid. Extraction is etfected usingthenoyltrifluoroacetone (TTA), 0.5 M in 200 ml. of diethyl ether. Thetwo phases are agitated for about an hour, and greater than 99% of thezirconium is extracted, while virtually all of the niobium remains inthe. aqueous solution. The solid catalyst is slurried in about twice itsweight of pure diethyl ether, and with constant stirring sufficient ofthe extracted zirconium-TTA complex solution is slowly added to providethe desired level of radioactivity. After about 30 minutes at theboiling point of around 34.6 C., the supernatant ether is siphoned off,and the catalyst dried by evaporation, heated to 200 C. for two hours toremove residual adsorbed ether, and, upon cooling, humidified with wetnitrogen for about two hours.

Hafnium-181 is available as hafnium oxychloride in one normal aqueoushydrochloric acid. It is impregnated onto a different catalyst by aprocedure exactly identical to that used in impregnating zirconium-95.

A third catalyst is impregnated with scandium-46, obtaina ble as thetrichloride in one normal hydrochloric acid. In this case, it isadvisable to pretreat the catalyst to be tagged with 100 p.p.m. ofcerium in the form of a TTA complex; cerous ion will extract intoTTA-diethyl ether from a neutral solution. The cerium extract is addedto the catalyst while being stirred in reflux ether prior to thescandium addition. Scandium impregnation follows the procedure forzirconium hafnium.

Gold-198 may be impregnated onto a catalyst as the th-iocyanate.Gold-198 is available as the trichloride in mixed hydrochloric andnitric acids. To ml. of the mixed acids solution is added an excess ofpotassium thiocyanate. The resultant solution is extracted three timeswith separate portions of 100 ml. of diethyl ether. Five pounds ofcatalyst is slurried in 6 liters of ether at reflux temperature and thegold extracts are added during stirring. Uniform quantitative depositionoccurs immediately. The ether is filtered off and the catalyst dried bygentle heating under a nitrogen sweep until it is again fluid.

Each of the foregoing procedures yields a catalyst which is uniformlyimpregnated with radioactive material. In tests of catalysts impregnatedaccording to the methods described previously, catalysts were screenedand fractions taken at 40, 50, 60, 70, 90, 120, and 145 micron screensize. The specific activity of each fraction was within 15% of theaverage specific activity, and in most instances was much less than 10%.Other impregnation procedures may of course be employed, either for thespecific isotopes described above or for other radioactive metals, andin this connection attention is invited to the previously cited Bailarbook. Coordination compounds, especially the organic compounds such asaspartic acid, ethylene diamine tetraacetic acid, in addition to TTA andthe like are especially preferred.

Tracer catalyst addition At the beginning of a test, a number ofdifferent catalysts, say competitive commercial cracking catalystsobtained from different manufacturers, are each tagged with aradioactive metal isotope having mutually distinguishable energyspectra. Known amounts, about mg., of each tagged catalyst and of themixture of all tagged catalysts to be charged to the fluid catalyticconversion unit are each separately mixed with two kilograms ofnonradioactive equilibrium catalyst and then sealed into a separatecounting can. These constitute the standard samples.

The larger portions of the tagged catalyst are then introduced intofluid catalytic conversion unit. Such introduction may be effected byconventional means well known to those in the art, e.g. by adding to agas stream passing into a cat cracker regenerator, or by slurrying withoil and introduction into a cat cracker reactor.

Counting techniques Within an hour or two after the several taggedcatalyst samples are introduced to the unit, a small portion of theunits inventory, say ten pounds, is withdrawn. It is necessary to waitsufficient time for the tagged catalyst to achieve even distributionthroughout the bulk of the inventory, but this usually occurs withinless than an hour or so. Thereafter, samples may be collected from theregenerator at intervals of about once daily during a test period, whichmay run for, say, forty days or more.

Sample counting is done with a Radiation Instrument DevelopmentLaboratory 200 channel pulse height analyzer (Model 3302) and a 5 /2" x5" NaI(Tl) scintillation crystal mounted with a light pipe to a 3"E.'M.I. photomultiplier. Catalyst samples to be counted are weighed intospecial ten pound sample cans fitted with a well to slide over thecrystal. The samples are counted for a given time, usually five or tenminutes, until a large number of counts accumulate in peak channels.

Each day the collected sample of the units inventory and the standardsamples of originally impregnated catalyst are counted. The results, asobserved on an oscilloscope screen, have a configuration resembling thatshown in FIGURE 1, although the figure is plotted on semi-log paper. Thecomposite spectrum represents the sum of the contribution from eachisotope in proportion to the concentration of that isotope in thecomposite. It will be observed that each peak on the compositecorresponds to a peak on either the hafnium, the silver, the zirconium,or the scandium curves for pure standards.

It will be understood that each of the curves is expressed on abackground-free basis. A background count may be made in the usual way,and the pulse height analyzer herein employed is capable of internallysubtracting the background count from each pulse channel.

Computation techniques After obtaining information such as that shown inFIGURE 1, it is necessary to determine the relative proportion of eachcatalyst sample, or in other words the contribution of each radioisotopein the composite. Direct curve subtraction may be employed where thenumher of isotopes is not excessive, but a computer technique has beendeveloped which vastly simplifies the determination while affordingsuperior accuracy.

All data from the pulse height analyzer is automatically printed out inthe form of a channel designation and a digit representing counts forthat channel in a unit time. This information is key-punched onto IBMcards and fed to an IBM 704 computer, together with informationrepresenting the background count. The computer is first set to subtractthe background count, channel by channel, from the samples and thestandards. Where due to statistical fluctuations negative results areobtained on subtraction, the result is set equal to zero for thatchannel. The background-free spectra are then compared by the computeras follows:

Let S (n) to S (n) be the counts per channel, n (0 n 200), for each ofthe four standards and n(n) be the same for a given sample. (The fifthor mixture standard is treated as a sample as a continuous check.) If Ato A are the relative amounts of the four isotopes in the sample then:

with the approximately sign indicating that because of statisticalfluctuations in the counting process the equality will not be exact forany channel. To determine the best values for the four A s, it isnecessary to minimize the R.M.S. error over the 200 channels withrespect to each All Where the denominator is chosen to account for thePoisson distribution arising in the counting process. Differentiation in(A2) results in four non-linear equations for the values of the A s,which cannot be solved explicitly. It is therefore necessary to solvethe approximate equation:

which upon differentiation and rearrangement gives the matrix equation:

By solution of (A4) four approximate values of the A s are obtained,call them A (1). These values are used to compute a new denominator for(A3), call it u (n):

and (A3) becomes for the second approximation:

6 4 aA.'E{ Z i i which may again be solved for a new set of values, A(2),

and the whole process repeated until some convergence criterion is met,say:

for all A The computer makes the above iteration to a programmedconvergenece criterion e. For normal samples, convergence to e=0.001occurs in about three iterations. The machine prints out the values ofthe A s computed for each iteration; convergence to even smaller valuesof e is rapid and generally non-oscillatory.

Once the relative amounts of the four isotopes in the sample aredetermined, by trivial material balance caloulations the amounts of eachoriginally impregnated catalyst in the units inventory are computed. Itmay be necessary to adjust the computations to allow for the addition ofmakeup fresh catalyst to the unit and the deliberate withdrawal ofequilibrium catalyst, but again such computations are conventional.

The results may be plotted on a chart of the type presented as FIGURE 2herein. This chart shows the results of testing three commercialcatalysts A, B, C, in a large commercial fluid catalytic cracking unit.It will be observed that catalyst A tended to remain longest in theunit, which is evidence of its superior attrition resistance. Catalyst Bis somewhat less resistant, while catalyst C is poorest in this regard.

The information obtained by the inventive technique possesses theadvantage of permitting loss determinations to be made of severaldifiercnt catalysts simultaneously. Thus, any effects on catalyst lossdue to such factors as deliberate or inadvertent changes in conversionor catalyst regeneration conditions and the like are experienced by allcatalysts simultaneously, and hence any variables other than theinherent physical stability of the catalyst ar compensated for.

The inventive system has numerous other substantial advantages. Withrespect to catalyst impregnation, any desired amount of radioisotopeconcentration may be employed, and no changes to the physical orchemical properties of the catalyst are encountered. The impregnationsystem is extremely versatile and can accommodate a considerable varietyof isotopes. The counting technique is accurate and convenient, and doesnot require any special equipment or unduly dangerous products, providednormal radiation safety procedures are observed. Also, by permitting theuse of relatively short half life isotopes, radioactivity soondiminishes to a negligible level. Furthermore, there is no need toaccount for radioactive decay, since this is compensated for byemploying standard samples and counting these at substantially the sametime as are the regular samples, e.g. within 24 hours, but preferablywithin the same hour.

From the foregoing description it is evident that we have provided anextremely facile method of determining catalyst loss, or retention,rates in fluid catalytic conversion units, together with a technique foruniformly impregnating the catalysts with radioactive tracers. While theinvention has been described in conjunction with specific embodimentsthereof, these are by way of illustration only. Many alternatives,modifications, and variations will be apparent to those skilled in theart in view of our disclosure, and accordingly it is intended to embraceall such alternatives, modifications, and variations as fall within thespirit and broad scope of the appended claims.

We claim:

1. A process for rapidly but uniformly impregnating a finely dividedadsorbent catalyst having varied particle size distribution with aradioactive metal isotope without any noticeable alteration of catalystproperties which process comprises forming a slurry of said catalystwith an inert volatile organic liquid, introducing into said slurry asolution containing said radioactive metal isotope in the form of asoluble coordination compound dissolved in said inert volatile organicliquid, the volatility of said liquid being such to permit its removalfrom the catalyst without the use of undue temperatures, intimatelymixing the slurry and solution at the boiling point of said liquid toobtain rapid but uniform impregnation of said catalyst 7 With saidisotope, removing excess liquid, and drying the resultant impregnatedsolid.

2. Process of claim 1 wherein said compound is a coordination compoundof t-henoyltrifluoroacetone.

3. Process of claim 1 wherein said isotope is zirconium- 95.

4. Process of claim 1 wherein said isotope is hafnium- 181.

5. Process of claim 1 wherein said isotope is scandiuni- 46.

References Cited by the Examiner UNITED STATES PATENTS 3,070,696 12/1962McEwen 250-106 5 OTHER REFERENCES Kinsella, Jr. et al.: Better CatalystLoss Studies, Article from Petroleum Processing, November 1955, 6 pages.

REUBEN EPSTEIN, Primary Examiner. CARL D. QUARFORTH, Examiner.

1. A PROCESS FOR RAPIDLY BUT UNIFORMLY IMPREGNATING A FINELY DIVIDEDADSORBENT CATALYST HAVING VARIED PARTICLE SIZE DISTRIBUTION WITH ARADIOACTIVE METAL ISOTOPE WITHOUT ANY NOTICEABLE ALTERATION OF CATALYSTPROPERTIES WHICH PROCESS COMPRISES FORMING A SLURRY OF SAID CATLYST WITHAN INERT VOLATILE ORGANIC LIQUID, INTRODUCING INTO SAID SLURRY ASOLUTION CONTAINING SAID RADIOACTIVE METAL ISOTOPE IN THE FORM OF ASOLUBLE COORDINATION COMPOUND DISSOLVED IN SAID INERT VOLATILE ORGANICLIQUID, THE VOLATILITY OF SAID LIQUID BEING SUCH TO PERMIT ITS REMOVALFROM THE CATALYST WITHOUT THE USE OF UNDUE TEMPERATURES, INTIMATELYMIXING THE SLURRY AND SOLUTION AT THE BOILING POINT OF SAID LIQUID TOOBTAIN RAPID BUT UNIFORM IMPREGNATION OF SAID CATALYST WITH SAIDISOTOPE, REMOVING EXCESS LIQUID, AND DRYING THE RESULTANT IMPREGNATEDSOLID.